The term “LIDAR” refers to a technique for measuring distances to visible objects by emitting light and measuring properties of the reflections of the light. A LIDAR system has a light emitter and a light sensor. The light emitter may comprise a laser that directs highly focused light toward an object which then reflects the light back to the light sensor. The light sensor may comprise a photodetector such as a photomultiplier or avalanche photodiode (APD) that converts light intensity to a corresponding electrical signal. Optical components such as lenses may be used in the light transmission and reception paths to focus light, depending on the particular nature of the LIDAR system.
A LIDAR system has signal processing components that analyze reflected light signals to determine the distances to surfaces from which the emitted laser light has been reflected. For example, the system may measure the “flight time” of a light signal as it travels from the laser, to the surface, and back to the light sensor. A distance is then calculated based on the known speed of light. As a result, reflected light failing to directly strike the sensor may cause the corresponding electrical signal to be weak or even non-existent. Therefore, the functioning of a LIDAR system can be affected by even small deviations in the alignment of the optical components. This is because the emitted light may travel great distances before being reflected by the object back toward the light sensor such that relatively small angular deviations of the light path may significantly affect the light sensors ability to detect the reflected light.